At the convergence of terrestrial, freshwater and marine realms, coastal river deltas are shaped by river inflows that deposit sediment and ocean tides and currents that disperse it. Gradients of salinity and submergence and dynamic substrates create shifting mosaics of channels, islands, floodplains, intertidal and subtidal mud plains and sand beds that may be regarded as embedded patches of other functional groups. The dynamic mosaics support complex foodwebs. Planktonic algae, aquatic plants and river inflows contribute detritus for in-sediment fauna. Fish and zooplankton are diverse and abundant in the water column, providing food for wading and fishing birds and marine and terrestrial predators.